The present invention relates to a submersible cable. More particularly this invention concerns such a cable usable in a fish-repelling installation.
It has been found possible to repel fish by passing massive current pulses through a submerged conductor. Such an arrangement is used around the water intakes of power plants and the like to prevent fish from being sucked up.
Such an arrangement is also used to prevent sharks from entering swimming areas. In this type of arrangement a cable is laid across a mouth of a bay or is made to encircle a beach swimming area. A high-current pulse generator is connected to the ground (water) and to one end of the cable so as to feed high-current electrical pulses into the cable. These pulses flow through the cable to the other end and thence through the ground back to the source. The pulse shape and sequence is chosen so that the current flows along the source in an envelope surrounding the cable. This electricity in the water repels fish highly effectively, as it affects the muscles of the fish in the same manner as an electric shock affects a human being. Fish are, however, substantially more susceptible to such electrical shocks than human beings.
Such a cable is typically formed as a conductive core provided with a conductor smoothing layer and formed of a metal. A highly insulating dielectric surrounds this core and a field-limiting layer as well as armoring is normally provided on the cable.
Nonetheless, such a submersible cable is often subjected to very active or corrosive chemical attack by the seawater and considerable physical attack by the surf or underwater currents. Furthermore, the electrical field created around the cable often only increases the chemical activity of the seawater so that the so-called water-treeing effect is produced. In accordance with this effect, tiny pinpoint or hairline passages form within the insulation of the cable so that conductive leaks occur, by which are meant conductive pathways through the insulating layer. Such leaks allow the return current frequently to follow the armor of the cable and, therefore, not to be effective in the water to repel fish. It is essential that the return current flow around the cable in the water, as only this type of current envelope can be used to repel fish in the desired manner.